1. Field of the Invention
Embodiments of the present invention generally relate to a subsea salvage operation using a lifting magnet.
2. Description of the Related Art
FIG. 1A is a cross section of a prior art sub-sea wellbore 5 drilled and completed with a land-type completion 1. A conductor casing string 10 may be set from above sea-level 15, through the sea 20, and into the sea-floor or mudline 25. The conductor casing 10 allows the wellhead (not shown) to be located on a production platform 30 above sea-level 15 rather than on the sea-floor 25. Alternatively, the platform 30 may service a subsea-type completion or a manifold from multiple subsea-type completions.
Once the conductor casing 10 has been set and cemented 35 into the wellbore 5, the wellbore 5 may be drilled to a deeper depth. A second string of casing, known as surface casing 40, may then be run-in and cemented 45 into place. As the wellbore 5 approaches a hydrocarbon-bearing formation 50, i.e., crude oil and/or natural gas, a third string of casing, known as production casing 55, may be run-into the wellbore 5 and cemented 60 into place. Thereafter, the production casing 55 may be perforated 65 to permit the fluid hydrocarbons 70 to flow into the interior of the casing. The hydrocarbons 70 may be transported from the production zone 50 of the wellbore 5 through a production tubing string 75 run into the wellbore 5. An annulus 80 defined between the production casing 55 and the production tubing 75 may be isolated from the producing formation 50 with a packer 85.
Additionally, a stove or drive pipe may be jetted, driven, or drilled in before the conductor casing 10 and/or one or more intermediate casing strings may be run-in and cemented between the surface 40 and production 55 casing strings. The stove or drive pipe may or may not be cemented.
FIG. 1B is a cross section of the platform 30 and completion 1 damaged by a hurricane. Hurricanes in the Gulf of Mexico have recently damaged or destroyed several production platforms 30 along with the completions 1. The production platforms and the completions 1 have sunk to the sea-floor 25.
FIG. 2 illustrates a prior art salvage operation in progress. A diver may be dispatched from a salvage vessel (not shown) to the wreckage. A remotely operated vehicle (ROV) (not shown) may be deployed instead of or in addition to the diver. The diver and/or ROV may cut the platform wreckage into manageable pieces 30p. The diver and/or ROV may also assist in flooding the wellbore 5 with seawater or other kill fluid and cut the casing assembly 1 at or near the mudline 25. The diver and/or ROV may then connect a piece 30p of the wreckage to a line from a crane on the salvage vessel. The connected piece may then be raised to the surface 15 and loaded on a barge (not shown) or other scrap vessel. Alternatively, the piece 30p may be moved to a debris pile on the sea-floor 25. The process may be repeated for the wreckage pieces 30p and the severed casing assembly 1. Once the larger pieces have been loaded on the barge, a basket (not shown) may be lowered to the diver. The diver may then proceed to pick up smaller remaining debris off of the seafloor 25 and load the debris in the basket. The basket may then be raised and dumped on the barge. The prior art operation is time-consuming, cumbersome, and may expose the diver or other salvage equipment to unnecessary risk.